1. Field
Apparatuses and methods consistent with exemplary embodiments relate to an objective lens for optical pickup and an optical pickup apparatus having the same, and to an objective lens for optical pickup in which an optical path changing element is provided in a non-effective region outside an effective region, and an optical pickup apparatus having the same.
2. Description of the Related Art
An optical pickup apparatus, as an apparatus for recording information on a disc or reproducing the information from the disc by using light, includes an objective lens for focusing the light irradiated from a light source on the disc.
There are various types of discs, such as blue-ray discs (BDs), digital versatile discs (DVDs), and compact discs (CDs), and according to the type of disc being used, an optical pickup apparatus is provided with an appropriate objective lens. An objective lens, which is compatible with BDs, DVDs, and CDs, is also in use. Hereinafter, such an objective lens is referred as a “compatible objective lens”.
The light irradiated from a light source is incident on a light source side lens surface of the objective lens. The incident light is not incident on an entirety of the light source side lens surface, but only on an inner region having a fixed diameter. The inner region is usually called an “effective region” or an “effective diameter”. For the sake of explanation, hereinafter, a region disposed outside the effective region on the lens surface is referred as a “non-effective region”.
For instance, by providing a barrel supporting the objective lens, the barrel having an aperture in a size corresponding to the effective region of the objective lens, the light irradiated from the light source can be guided onto only the effective region. However, due to factors, such as design tolerances of the objective lens and the barrel, deformations due to use of the objective lens and the barrel, assembling tolerances between the objective lens and the barrel and the like, the light irradiated from the light source may be partially transmitted onto the non-effective region (outer region) of the light source side lens surface.
In the non-effective region disposed at an edge of the objective lens, the lens surface may have a relatively large slope, as compared to a slope within the effective region, which is disposed at a center of the objective lens.
Accordingly, if the light is incident onto the non-effective region, light transmitted by the objective lens may become deteriorated or degraded due to aberrations. Such a deterioration or degradation may be more intensified in an objective lens for use with a BD or in a compatible objective lens having a relatively large numerical aperture (NA).